The initial clinical experience with simultaneous small bowel/liver transplantation (SBL) suggests that liver grafting may protect the small bowel from rejection. A pilot study of SBL in DA (RT1a) rats with Lewis (RT11) allografts in our laboratory provided experimental support for this concept. However, the clinical applicability of the data was questioned because the transplants were performed in a low-immune-responder rat strain combination. This study examined the outcome of SBL in several rat strain combinations. Isolated small bowel transplants (SB) and SBL were performed in three groups: DA→PVG (low immune responder), BN→LEW (intermediate immune responder) and ACI→LEW (high immune responder). Lewis→Lewis isografts were used as controls. All of the rats with SB rejected their allografts, whereas all of the rats with simultaneous liver grafts had minimal or no signs of intestinal rejection. The outcome of SBL was profoundly affected by the donor-recipient strain combination. The low immune responders developed severe graft-versus-host disease. The intermediate immune responders developed mild-to-moderate GVHD and moderate liver rejection. The high immune responders developed severe liver rejection. In this study, the outcome of small bowel transplantation depended upon the strain combination used and whether or not a simultaneous liver graft was transplanted. The immune interactions that occur after multivisceral transplantation are complex and cannot be easily predicted.
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